nm-applet: trouble with bridge connections

[roger tarani free fr]

Hi

Debian 10/gdb
network-manager                   1.14.6-2     amd64
network-manager-gnome             1.8.20-1.1   amd64


I create a bridge with nmcli.
I delete the previous wired connection.
The networking setup is fine and the bridge connection even appears in the GUI Settings/Network Wired section.
As confirmed by the CLI:

$ nmcli connection show 
NAME                  UUID                                  TYPE      DEVICE  
br0                   f8cc5703-e3ba-4afb-b7e6-75fd995cee16  bridge    br0     
bridge-slave-enp0s25  cef1a1ae-2d51-46b5-aa9d-81227a8c9be3  ethernet  enp0s25

But if I "deactivate" this connection from the GUI, it totally disappears (from the GUI), and the networking 
setup is put down.
In fact, it has the same effect as doing 'nmcli connection down bridge-slave-enp0s25' :

$ nmcli connection show
NAME                  UUID                                  TYPE      DEVICE
br0                   f8cc5703-e3ba-4afb-b7e6-75fd995cee16  bridge    br0   
bridge-slave-enp0s25  cef1a1ae-2d51-46b5-aa9d-81227a8c9be3  ethernet  --    


I found two ways for reactivating the bridge connection:
  $ sudo systemctl restart NetworkManager.service
or
  $ nmcli connection up bridge-slave-enp0s25

The networking setup goes up and the bridge connection even appears again in the GUI.

Do you know a simple way or a workaround to fix that?
Or should we consider this as a flaw in the network-manager-gnome package that need to be fixed?

PS
When one creates a wired connection from the GUI Setings/Network, if he comes bask and changes some 
parameters (IP address, ...) then clicks on Apply, it is in fact ONLY saved to a file in 
/etc/NetworkManager/system-connections/<connection-name> but it is NOT applied.
To apply a change, one must click on the slider button to put it down then again to put it up (or use 'nmcli 
conn down <connection-name> && nmcli conn up <connection-name>' ).
I had some pain with a new Debian Buster setup before I could figure out what happened there.
If this is an expected behaviour? If yes, can you add a warning to explicitly inform the user that he MUST 
click twice on the down/up slider button for getting the connection down and up and his changes applied?
I would clearly prefer to get a button 'Save' and a button 'Save & Apply' 
(or even a third button 'Just Apply' taht would be nice for quickly testing some parameters - but it would 
make the GUI a little bit unusual ; or an 'expert mode' could be added) 

Thanks
Best regards